1. Field of the Invention
This invention relates to a device for opening and closing a screen cover for a television receiver for selectively displaying plural types of images with different aspect ratios which is arranged on the front side of the television screen of the television receiver and which is adapted for opening or receiving left and right sides and upper and lower ends of the screen in association with the different types of images.
2. Description of the Prior Art
Recently, a move towards widescreen telecasting (so-called high-vision system) system is proceeding. If such system is realized, a television screen with a 4:3 aspect ratio co-exists with a 16:9 aspect ratio.
For receiving the high-vision telecasting by a television receiver of the standard system, such as the NTSC system, PAL system or SECAM system, with the aspect ratio of 4:3, for displaying the image, left and right portions of the high-vision system screen are discarded to effect display in conformity to the current 4:3 system, or the high-vision system screen is compressed both horizontally and vertically so that the screen with the 16:9 aspect ratio is adapted to the 4:3 standard system television screen.
With the former, only parts of the image transmitted by the high-vision system are displayed. Thus the latter system, according to which the high-vision system image is compressed and adapted to the current screen with the aspect ratio of 16:9 remaining unchanged, is more desirable.
On the other hand, if the current telecasting is to be received with the widescreen television receiver with the aspect ratio of 16:9 for displaying the television image, it may be envisaged to use only the portion corresponding to the aspect ratio of 4:3 without using left and right panel portions of the screen.
Although it may be contemplated to cause the redundant screen region not to emit light, since the deterioration of the light-emitting elements of the television screen, such as phosphors, differs between a screen region where the image is perpetually displayed (common screen region) and a screen region other than the common screen region, or the non-common region, these two regions differ in luminosity when the image to be displayed on both of these screen regions is displayed.
In this consideration, it has been proposed to provide such television receiver with a screen cover openably closing the non-common screen region so that, when only the common screen region is in use, the non-common region is closed by the screen cover and, when the entire screen is in use, the screen cover is moved to a position of opening the entire screen surface.
FIGS. 1 and 2 illustrate two examples of the screen cover opening/closing device 100 provided with such screen cover.
It is noted that the screen cover opening/closing device 100, shown in FIGS. 1 and 2, is adapted to open or close left and side panel portions of the television screen.
Referring to FIGS. 1 and 2, 101 is a Braun tube, 102 is a phosphor surface of the Braun tube 101, a is a region of the phosphor surface 102 exclusive of both side panel regions b, b thereof, that is a common region, in which the image corresponding to the current television system is displayed. 103, 103 are flexible screen covers separately arranged at left and right side panel regions of the Braun tube 101. Referring to FIG. 1, the screen covers 103, 103 are movable between a first position in which one ends 104, 104 thereof face the left and right panel portions b, b on both sides of a center panel portion a of the phosphor surface 102, as shown in FIG. 1, and a second position in which the ends 104, 104 are moved away from the phosphor surface 102, along a path of movement by being guided by suitable guide means, not shown.
105, 105 are spools to which are separately fixed other ends 106, 106 of the screen covers 103, 103 and which are rotationally driven by driving means, not shown. The screen covers 103, 103 are moved by rotation of these spools 105, 105.
When the spools 105, 105 are rotated in predetermined amounts in the screen cover take-up direction, from the position corresponding to the first position of the screen covers 103, 03, these screen covers are moved to the second position shown in FIG. 2, for opening the phosphor surface 102 in its entirety. In this position, the images of the high-vision screen are displayed. If the spools 105, 105 are rotated in the opposite direction, that is in the direction of reeling out the portions of the screen covers 103, 103 taken up on the spools, the screen covers 103, 103 are moved to the first position shown in FIG. 1, so that the left and right side portions b, b of the phosphor screen 102 are covered by the screen covers 103, 103. The images of the current television system are displayed in this condition on the television receiver.
With the above described screen cover opening/closing device, since the spools 105, 105 are spaced apart from each other on both sides of the screen, two separate driving sources need to be electrically synchronized with each other, or a single driving source needs to be mechanically connected to each other for synchronization.
If the spools 105, 105 are not mechanically synchronized with each other, but simply electrically synchronized with each other, the screen covers 103, 103 may be moved differentially, in which case the opening degrees will be different between the screen covers 103, 103.
On the other hand, if the spools 105, 105 are mechanically synchronized with each other, although there is produced no difference in the opening degrees of the screen covers 103, 103, the driving source needs to be connected to the spools with the Braun tube 102 in-between to lead to complicated and bulky construction.